Lines



F. ALDENDORFF.

ELCTROMECHANICAL SWITCHING SYSTEM FOR-INTERCONNECTING TELEPHONELINES. ,xPPL'lcA-Twu'.HLgpu-MN..261914.

Witnesses:

F'. ALDENDORFF.' ELECTHOMECHANI'CAI. SWITCHING SYSTEM FOR INTERCONNICTIIIG TELEPHONE LINES.

APPLICATION FILED IAN.26. 19H4. 14:

YSHEETS-SHEET 2.

WInesses: InvenIOr':

F. ALDENDURFF.

" ELECTRO'MECHANICAL SWITCHING SYSEM FOR NTERCONNECTING TELEPHONE LINES.

APPLICATION HLED 1AN.26. |914.

F. ALDENDORFF.

l ELECTROMECHANICAL swlTcHlNG sYsEM Foa INTERCONNECTING TELEPHONE UNES:

APPLICATION FILED IAN.26. 1914. A

Patented 0ct.14,1919.

TSHEETS-SHEET 4.

InvenI'or:

WInesseS:

F, ALDENDORFF. ELECTROMECHANICAL SWITCHING SYSTEM FOR'INTERCONNECTING TELEPHONE LINES.

APPLICATION FILED IAN.26. I9I4. 1,319,031 I Patented Oct. 14, 1919.

SHEETS--SI'IEET 5.

Saou bano Cano bano L I /Caoo HS v (2,* OO aIw 217 o 1' Y l Wa "o I 9 s ,20u i- .y o l O l ,2m I

lvm vgLvvIh-k/MB L wI'neSSeS: InvenI'orz F. ALDENDORFF.

ELECTROMECHANICAL SWITCHING SYS-TEM F.0R INTERCONNECTING TELEPHONE` LINES.

i APPLICATION FILED JAN.26.1914.

1,819,031. i Patented 00111-1919.

7 SHEETS-SHEET 6.

Wil'nesses: l .I lnveni'or:

UNITED sTATEs PATENT oEEioE.

FRITZ ALDENDORFF, 0F WILMERSDORF, BERLIN, GERMANY.

ELECTROMECHANICAI' SWITCHING SYSTEM FOR INTERCONNECTING TELEPHONE- A LINES.

Specification of Letters Patent. Patented Oct. 14, 1919.

Application filed January 26, 1914. Serial No. 814,451.

To all whom t may concern.'

Be it known that I, FRITZ ALDENDOREF, a subject of the King of Great Britain, residing at 32 Mannheimerstrasse, Wilmersdorf, Bei-lin, Germany, have invented certain new and useful Improvements in Electromechanical Switching Systems for Interconnecting Telephone-Lines, of which the following is a specification.

My invention relates to electromechanlcal or automatic or semi-automatic switching systems.

An object of the invention is to economize ers and connectors are known, but the novelty in the scheme described herein consists in the manner in which the trunks or Ilink circuits are connected to these switches and in their specific arrangement and circuits. They are provided with sets of fixed contacts connected to subscribers lines and with a set of movable contacts or brushes capable of tacts of a group selector finder. t

brushes of each two-way switch 1s connected being brought into contact with any of their sets of fixed contacts. From the set of brushes of each of these switches (which will henceforth be called two-way switches because they extend connections from calling subscribers to a trunk and at other times from a trunk to a subscriber) one trunk or link circuit leads to the movable contact,

arms of a group selector or a selector finder and another trunk leads to the fixed con- The set of while the switch is in its normal position to the movable contact arm of the group selector or selector finder with which it is associated. But as soon as the two-way switch is to be used for establishing a connection with a wanted subscriber its brushes are disconnected from the contacts arm of the group f selectors while others are connected to groups selector finders which establish connections with free group selectors.

The two-way switches are started or set inv motion one after the other by starting impulses sent through a starting circuit in the order in which the calls are made by the calling stations.

The moment a subscriber calls the battery lead to the calling or line circuits of the other subscribers is opened by a lcall regulator until a connection is made between the calling subscriber and a grou-p selector or connector. The line relay of each subscriber has a locking circuit which is closed the moment the subscriber calls in order to render the calling circuit of this subscriber independent of the common battery lead which is opened immediately after the call is made.

Whenever a two-way switch is moved out of its normal position in order to establish a connection with a calling line the starting circuit is disconnected from this switch and is immediately after extended to the next two-way switch. This also takes place whenever a two-way switch is used for connecting for a wanted line. For these two cases two special switches are provided one of which is shifted by the two-way switch itself yas soon as it is moved out of its normal position, the other beingshifted independently of its twoway switch by a current from a group selector over the trunk leading to the two-way switch.

The starting circuits of the two-way switches are arranged sothat the starting of several switches 'by the same starting impulse is impossible. This is accomplished by' arranging the switch that extends the starting circuit from one two-way switch to the next so that the starting circuit is extended only after a starting impulse has ceased flowing. The extending switch has va spring which is tensioned by a magnet excited by the starting impulse and which only exerts its force so as to shift the extending switch after the starting impulse has ceased iiowing.

In large exchanges the subscribers lines are divided into groups and each group of lines is connected to a group of two-way switches. The groups of subscribers lines are sub-divided into sub-groups, Each two? way switch is composed of two,l 'inders, a primary and a secondary finder.;y The Aprimary iinder finds the calling line and the ioo` ' selector or link circuit. If there are ten sub-groups and ten lines in each sub-group the'greatest number of steps to be taken by the primary' and secondary finders will be -ten yand as both finders act simultaneously the maximum time required for finding any particular line out of 100 is the time that' the brushes of a finder take to travel the distance occupied by ten adjacent sets ofv contacts.

When a two-way switch is used to make a connection with a wanted line the circuits of the motor magnets of the primary and secondary nders of the switch, which are ordinarily connected to a common circuit,

are separated and the motor circuits are then controlled separately by the person setting up the connection with the aid of switch controller. v

The primary and secondary motor circuits of a two-way switch are separated also when restoring the. switch to its normal position. The two-way switches are each provided with two' test relays, one for the primary finder and another for the secondary finder, which open the circuits of the finder motor magnets the moment they find the proper permutation wire. These test relays lare made inoperative when the two-way switch isg'used to connect to a wanted line.

Another feature of the invention consists in an impulse repeater located at a group selector at whichimpulses arising in one portion of a circuit are repeated in another portion of the circuit, the second portion being normally disconnected by open conthe first and the ,open contactsv tacts from not being closed until the called subscriber in responding to the call changes'the strength .y

of the ringing current sent to him from a group selector.

In order to simplify the circuits of the last' selector in an established connection (i. e.,

of the selector or connector that makes con-l nection with the wanted line) no circuits are used in this selector which act 'backwardly on the impulse repeater atthe group selector. A called subscriber in responding to a call iniuences the impulse repeater at the group-selector'without the aid of any. in-

tervening devices or circuits placed at the last selector. vThisis accomplished by tentain my apparatus.

tively applying a source of ringing current through a ringing control electromagnet or relay located at the group selector to leads extending through a chain of selectors to the wanted line. 'The arrangement of the ringing control circuits is such that, if the wanted line is busy and the test relay in the last or final selector is not excited, no ringing current flows through the said ringing control magnet on account lof the ringing c'urrent path to thewanted line not having been closed by the said test relay.. If the line is busy the ringing current does not How. Whether the ringing current remains connected to the leads or not is made dependent on its flowing immediately after it is connected to the leads. 1f the ringing current does not immediately commence fiowing a relay at the group selector which effects the steady application of the ringing current to the leads fails to be energized and the momentarily applied ringing current is then disconnected by the detraction of the armature of a slow acting relay. If the relay which causes the steady application of the ringing current is energized it closes the circuit of a ringing cut-ofi relay. The ringing current passes through the windings of this relay but does not cause it to attract its armature until the called subscribed responds to the call and causes a strengthening of the ringing'current. When the ringing circuit ofv a connecting relay which closes the contacts that separate the calling half of the circuit from the calledhalf and also prepares 'a meter circuit which is closed when the connection is broken at the end of theconversation. The energization of the. ringing cut-ofi also results in the cutting olf of the ringing current. v The invention is illustrated in the accompanyingdrawing in which Figure 1 shows the general connecting plan of the new system. Fig. 2 shows the' circuits of the subscribers line relays, the arrangement of the permutation or guide wires of the two-way switches and the arrangement of the call regulator. Figs. 3 and 4 illustrate the circuits ofthe two-way switches which perform the two functions of connecting a calling line to a group selector and of connecting a trunk leading `from the fixed contacts of a group selector to a wanted line. Fig. 5 shows the circuits of the selector finders designated HS in Fig. 1. Fig. 6 illustrates the circuits cfa first group selector with an y impulse repeater and Fig. 7 shows the circuits of 'a second group selector; `By placing Figs. 2 to 7 beside each other with Fig. 2 at the left and Fig. 7 at the right end a diagram of the Icomplete system forming the subject of this invention will be obtained. Figs. 8 and 9 illustrate certain contacts used the first hundred group.

In Fig. 1 the three rst groups of one hundred subscribers off an exchange for 1000 lines are diagrammatically indicated. To the right of the bracket I are indicated the switching apparatus VSI HSI and GWI of The switching apparatus of the second and third hundred groups are shown at the right of the brackets II and III.

It will be assumed that there are 15' twoway switches (only ten shown) in each roup which in the cases of calls coming from the subscribers S to the exchange connect the vcalling subscribers to free group selectors G Wl and in the casesy of connections extended by group selectors G W to trunks h1, h2, etc., connect these trunks to the lines of the wanted subscribers.

Each two-way switch V S is shown by three arcs 1, 2, 3 and a movable contact or brush 4. Each arc 1, 2, 3,is supposed to represent a row of ten sets of fixed con-- tacts. In reality each two-way switch has ten rows 'of ten sets ofcontacts in each but to simplify the drawing and description only three rows are indicated.`

The lines of three subscribers SI1, SI2, S13- S111, SH2, Suf-S1111, SH12, Sm3 connected to the third contact rows of the two-way switches are indicated-` r Of the 15 two-way switches in each group 5 are connected directly to group selectors -2 selectors G W1.

G W and 10 are connected to group selectors by means of selector finders H S to any idle one of a group of HSII test first the lower 5 group selectors G WH, then 3 lselectors G WIII and finally SIII test first five selectors G WFH, then 3 G WI and finally two G WH. l

Of the contact rows ofthe group selectors three only are indicated by the arcs p, 8J;

each row of contacts Ais multiply connected to a trunk cable h1, h2 which contains the trunk wires leading to the fifteen movable contacts 4 of the particular group vof thel two-way switches.

The trunk cable h1 leads to the two-way switches V SI of the first hundred group, the trunk -cable h2 to the two-way switches V SH of the second hundred and h, to the switches V Sm of the third hundred, etc.

The path of a talking connection through the system will now be illustrated: Suppose a subscriber SI calls. The brush 4 of a disengaged two-way switch will immediately 15 group selectors. y The latter group 1s made up of 5 group The selector finders H' cable h2.

' The group selector now hunts automatically for a free two-7 wayA switch V' Sn. When this is found the-person controlling the switches'causes the brush 4 of two-way will be either direct or v switchV SH to be moved into contact with the wanted subscribers line, e. g. S113.

As'the :two-way switches V S are'used both for outgoing connections originating at' the subscribers stations and for incoming'.

connections which come rtoI the subscribers stations from other stations and serve the double purpose ofline nders and connectors, a considerable saving'ofl switches is accomplished. v

Inthe known systems in which' separate line finders and connectors are used it will happen that all the line finders of a grou `are busy while some of the connectors othe group `are still free. Further calling subscribers would not be able to make connections as all the line finders are busy. Buil in the new system with"- two-way switches that will do the work .of line finders or connectors according to the requirements of the moment the further calling subscribers will still be able to make connections aslong as anyV twoway switches' are idle. If at vany momentthe demand for, connectors is in excess of the demand for line finders this demand will be supplied in a similar way.

Thus with the same numlber of switches dredg roup is sub-divided into tens, groups and 11, S12 represent the first two subscribers of the first tens group, first two subscribers of th'e second tens group and S31, S32 the first two subscribers of the third tens group. The other subscribers are omitted in order to simplify the drawing.

If the subscriber S12 calls, his line 12a 12b must be connected through the movable contacts 5a, bb, bef-bal, Z251, 501 of the two- -way switch, Fig. 3, to a trunk line oa, fob, vc

which leads directly or indirectly (through `a selector finder H S, Fig. 5) to a first group selector G WI. V

The brushes ba, bb, llcbah bbl, 501Y of the two-way switches V -S are set or guided to the positions in which they establish a vto' . tact connection between the trunk fva, vb, uc and the calling line (represented in this case by theI contacts K S12) by guide wires or permutation wires pu, pt.

The guide wires are divided into two groups pu, pt one of which guides the primary finder to the contact representing the calling line, the other guiding the secondary finder to the contact representing the tens group i'n which the-calling line is contained. When a subscriber calls, his line relay e. g, Z731 is energized and it earths one wire in each of the groups of guide wires pt and 79u thus setting up a circuit combination which will cause the pro-per motions of the primary and secondary finders of the next free twoway switch in the particular hundred group for connecting the calling line to a trunk.

The calling ofthe subscriber S12 z'. e. the

second subscriber in the first tens group, re'

sults in the contacts 100, 101 of his line relay Zr earthing the first wire 111 of the tens group of cuide wires pt and the second wire 21 of the units group of guide wires. If the subscriber 11 calls his line relay Conta-cts earth the first tens guide wire 111 and the first units guide wire 11. A call from subscriber No. 21 would result in the earthing of the tens wire 211 and the units wire 11 and so forth, so that a certain combination of earthed guide wires corresponds to each of the hundred subscribers of the group. i

In Fig. 3 only the circuits of one two-way switch V S is shown but the permutation or guide wires 2925, pu lead to all the two-way switches of the hundred group are connected to each of these switches by branch wires 'w17 w25 was wia we pla p27 pas 204 p5' The contact seits 7c s of the two-way switches of a group are connected in multiple.

From the common call regulator A R of each group a starting wire S W extends to the first two-'way switch V S. As soon as this switch is taken into use the starting wire S W is extended lthrough a swi-tch 101 or 103 to an extension starting' wire S W1 which leads to other switches similiar to 103, 104 on the next two-wayswitch, If the second t\voway switch of the. group is also engaged the starting wire is lextended to the third two-way switch and so forth.

The primary finder of each two-way switch has ten sets of three brushes each be, 5?), bc and a guiding brushv pb, all these' brushes being driven so as to brush past sets of contacts zsv respectively and single contacts K by a commonk driving shaft D.

If the brushes are moved so as to make the guiding brush pb rest upon the guiding con- 712 each of the sets of brushes ba, 5?), bc willi): rest upon the second sets of contacts 7c3 in the, row of contact sets ks, 1 kam, 70.91 etc., that it rides over. If the brush ya?) were to be moved to the fourth guiding contact f.,

each ofthe sets of brushes Da, bb, bc would also be moved to the fourth set of contacts ks in its particular row and so forth.

The common driving device that moves all the brushes consists of a ratchet wheel Z R fixed to a shaft D which is rotated step by step by a pawl cZ oscillated by an elec tromagnet- E. M.

The shaft'yD also shifts a switch O S1 vwhich while the two\\'ay switch is in its neet-ed to the 'trunk is selected by the secondary inder ZlV which has ten sets of fixed cont-acts K2 of four contacts each anda set of four movable brushes M1, 551, 501, sb. The set of brushes M1, Z151, 501, s?) is driven in any suitable manner e. g. by a shaft D1 which is turned .with the aid of a ratchet wheel Z R1 by a pawl K L1 oscillated by the armature A m1 of the secondary finder driving magnet Z M.

rfhe chain of events which happen when a subscriber calls and establishes a connection with another subscriber will now be explained.

Suppose subscriber No. S12 calls and establishes a connection withthe subscriber No. 31165. l

On raising his receiver from his switchhook the calling subscriber causes the two limbs 12a, 12b of his line to be connected in a well-known manner and a current then flows through the subscribers loop the path of' which may be traced from the battery B through the armature 112 of the call regulator, thence through 113, 114, 12a, S12, 12b, 115 to earth. The line relay Z132 attracts its armature closes a locking circuit for itself through the contact 116. By closing its contact 117 theline relay closes the circuit of the call regulator A Rl (battery B, A R, 117, earth) and this attracts its armature and by opening the contact 112 opens the common battery feeder of all the line relays of the, hundred group to which the calling subscriber belongs, so that no other subscriber of the same group can make a call by closing his loop and energizing his line relay until a two-way swit-ch V S has connected the first calling subscriber to a group selector. The connecting operation of the twoway switch will. however, not require more than about i a second so that if the second subscriber calls immediately after the first the delay in taking up his call will be so short that he will not notice it. The purpose of the momentary cutting off of the battery feed to all the subscribers eXce t the rst to call is to prevent a mixing of t e calls anda wrong setting of the two-way switches which would be possible if more 'than one call were passed on the two-Way switches at a time. .For this reason they sequence in which the calls are passed on over the starting wire S 1V is regulated so that the calls are transmitted over the starting Wire one after the other.

By its contacts 100, 101 the'line relay Z112 earths the first tens guide wire 111 and the second units guide wire '21 so that the contacts 7:2 and z in all the two-way switches of the group will be earthed and the points indicated where the brushes sb and pb of the particular two-way switch used. are to stop.

The call regulator in attracting its armature causes a momentary closure of the contact 119, 120. The .armature 1118 brushes past the spring 119 and momentarily presses 119 against 120. When the armature falls back into its normal position 119 is pressed away 120 and no closure of Contact 119, 120 takes place.

It is thus seen that the moment the subscriber S12 calls a current impulse is sent by the momentary closure of the contact 119, 120 ,from the battery B through S W. If the two-way switch V`S is idle this impulse will flow 'through 103, 111, 154, 104, 109, 155, 118, 156 to 157. Ac the point 157 the` starting impulse divides into three parts the one part flowing through 131, 158, motor' 1 magnet Z M of the secondary nder, 159 to earth and another part through 131, 160, 115, 161, 162, motor magnet E M of the primary finder, 163 to earth and the third part through 164, 135. ha, 200, 201, 203, starting relay to earth. The. magnets Z M and E M attract their armatures and each shifts its pawl (cl and cZl) into the next tooth of its ratchet wheel Z R, Z R1. When the starting impulse through contact 119, 120 ceases the pawls cZ and M1 are drawn back to their normal positions by their springs' 165, 166 and the ratchet wheels Z R, Z R1 are turned one step as a result of which the sets of brushes ba, bb, bc and the brush pb and also the brush set bal, bbl, bel, sb are two-Way switch.

The motor magnets of the started twowayl switch will now be energized by current impulses which flow from the negative pole of the exchange battery through 168,

105, 10s, 155, 11s, 156, 157, 151, 15s, z M,

159 t0 earth and through 131, 160, 115, 161, 162, E M, 163 to earth respectively. As soon as the brush pb reaches the contact k2 0f the second units guide wire 21 which is earthed by the armature Contact 101 a current will flow through the test relay p7' from the negative pole through 117, 169,

151, 17o, pr, 171, p5, 52, 21, '172, 101 to the The test relay pr is eneris earthed bythe armature contact 100, a

current will liow through the secondaryy test relay sr from the ne ative pole through 117, 169, 131,1 17o, a, 1 1, 85, pz, 111, 173,`

100 to earth. This will energize the secondary test relay which will open motor magnet circuit thus lcausing the set of brushes bal, bbl, bol, 5b to stop at the first contact set 7a2.

In the case assumed in which the twelfth subscriber of the hundred group is calling the circuit of the secondary finder magnet will be opened immediately after the starting impulse has flowed, because the moment this impulse ceases the brush set bal, bbl, bol, sb will be advanced to the first .set of contacts k2 of the Secondary finder.v

The rst contact set kc' is connected to the first set of brushes ba, bb, bc counting from the right, so that the calling subscriber S12 will now be connected through w12, b12, 012, R812, the first set of brushes ba, bb, bc, the first contact set e, brush set bal, bbl, bol to the trunk ca, cb, 00.

' The moment the test relays pr, 87' are both energized, the contacts 132,' 133 will be closed and a current will flow from the negative pole through 132, 133, 125, conn necting relay tr, 124 to the positive pole. The relay tr closes its contacts 141, 142, 143 and thus extends the Wires ca, vb, ce to the-wires 'van ob1, ce1. The relay tr also closes and opens a number of other contacts, but these are only of importance when the two-way switch V S is used as connector and need not be regarded in connection with the line finding 'operation of the two-way switch.

It was mentioned above that the starting relay 205 of the selector finder H S,Fig. 5, was energized at the same time as the motor magnets E M and S M by the starting impulses sent through the starting wire S fw at the moment the subscribe-r S12 called.

.Whenthe relay 205 is `energized the coning magnet 206 now rotates the brushes wa,

.con

Ytrunk m2, co2, 1202 leading wb, wc by a ratchet and pawl arrangment in a Well known manner causing them to brush over the fixed contacts connected to the trunks fvaz, co2, 'vez until an idle trunk is reached.' A current then flows from the negative pole through 208, 211, p r h, w c, o c2, relayc 1, 219 to earth. The relays p 1 h and e 1l are energized. The relay p 1| k opens the circuit of the motor magnet 206 at its contact 210so that thebrushes wa, wb, wc stop on the fixed contacts connected to the to an idle first selector G W1. By its contact 212 the test relay'closes a locking circuit for itself which is independent of the Contact 208 and at its contact 213 it opens the circuit of the starting relay 205. By its contacts 214, 215, 216 the test relay extends the line of the calling subscriber to the first group selector G W1. The relay p 1' it opensthe contact'217 and thereby prevents a premature release ,impulse from flowing from the earth through 209, 202 to the release wire a Z. By the open-v ing of contact 200 unnecessary oscillations of the armature of the starting relay are prevented which would be caused by impulses flowing from the interrupter 168 through 108, 155, 118,156, 161, 135 and h a.'

When the calling line is extended to the group selector bythe closure of the contacts 214, 215,216 the cut-of relay 01,2 of the calling subscriber is energized by a current flowing from the positive pole of the battery through 219, e 11,Fig. 6, o c2, 'w c, 216, o c1, 123, 143, o c, b c1, b c, cl2, c112 to the negative pole. Through the test relay p1 h and the cut-oil" relay c 1112 being connected in parallel the test potential on the test wire 11 c2 is lowered to such an extent that further test relays p 1 it Which may |be brought into connection with the trunk mtg, @712, U02 will now not receive sufficient current to energize them so that the trunk fva, 052, oc, will appear engaged.

.By the energization of thecut-o` relay 01" the' line relay Z112 is cut off from the calling line. On the deenergization of the line relay .31'12" the earth connections of. the

guide wires 111 and 21 are removed and at ,the same time the call regulator A R is deenergized by the opening of Contact 117. 1V hen the call regulator is denergized it does not close the contact 120, 119, but it calling subscriber and the group selector only amounts to a fraction of a second so that the likelihood of two calls-.waiting to be taken up is extremely remote and if it occurs the second subscriber to call will notlnotice any delay.

As soon as the earth connections of the guide Wires 111, 21 are removed through the cutting of of the line relay Z112 the circuits of the test relays p1", sr will 'be broken and the contacts 163, 159 in the circuits of the motor magnets E M and Z M will be closed. But these circuits will now be kept open at the contact 131 of the connecting'relay t 1. It has been said that when the brushes wa, wb, wc are caused to stop on the .idle trunk 'm2, wb2, rc2, a relay c 11 is energized that is associated with this trunk. The relay e 1a serves tovclose Athe battery circuit of the relays 1I 11 and c 1^. The relay c 1a is a circuit shifting or change over relay which changes over the group selector from its selecting to its trunk hunting or testing function. The relay 11 1n is a release relay which closes the release circuits of the selectors when the subscriber replaces his receiver on its switch hook.

The'relays 1q 1a and c 1a the periods of time during which the armature of the line control relay travels from one extreme position to another. The relays 1f 1' and c 1 are energized by opening contacts 232 and 233 and thereby opening paths of low resistance by which they are usually short-circuited. For this reason the battery circuits of these relays must be closed before the selecting impulses commence actuating the line control relay 280. 'Inis closure is effected by the contact 220 of the relay c 1".

On the calling line being extended to the trunk line fvaz, '0712, oc, the line control relay 280 is immediately energized by a current flowing from the negative pole of B1 through the lower winding of 280, wb2, wb, 214, obl, 121, 142, ob, bbl, bb, Z112, S12 121, am, ba, bal oa, 141, 119, 00.1, 215, wa, 'm2, upper winding of 280 to earth.

Justbefore the energization of relay 280 the relay c 1' was energized by a current flowing from the negative pole through 220, 232, c 1' to earth. In attracting its armature the relay (fr lets the spring 236 press against the contact spring 237. On the energization of the relay 280 the relay is short circuited by .Contact 233 and allows its armature to drop are energized in y momentarily connected to the change over circuit 29.0. 'This circuit is, however, still open at the contact 238 so that so far no shifting of circuits will be caused by applying the negative battery pole to the wire 290 belonging to the change over circuit.

When the relay 280 is energized the relay 7' r is energized by the opening of its short circuit at contact 232 the current flowing through fr r from the negative pole through 220, r r, 233 to earth.

As the calling subscriber desires a connection with subscriber No. 3465 he will work his switch cont-roller in a well known manner so as to first cause three openings of his line loop in rapid succession. This will cause three oscillations of the armature of the line control relay 280. During these oscillations the relays r r and c 7' are short circuited only for very brief moments for the contacts 232, 233 are adjusted so as to be closed only whenever the armature of 280 has moved to its utmost limit. These brief short-circuitings of the relays r 1' and c r a're not suflicient for these relays to allow their armatures to fall back so that they keep them attracted.

Each time the armature of 280 drops back a current impulse is sent through the vertical magnet 246 of the up and around group selector from th'e negative pole through 220, 231, 234, 224` 246 to earth. The vertical magnet 246 lifts the wipers of the group selector, which will be assumed to be of the Strowger type, to its third row ofl fixed contacts.

Aft-er the three thousand selecting impulses have thus beensent i'n by the three rapid openings of the calling subscribers line loop this loop remains steadily closed for a while until the subscriber sends in the next series of impulses for selecting the wanted hundred. The steady closure of the line loop causing an attraction of the line control relay armature and the change over relay `0 r will then be short circuited long enough to cause it to release its armature. During the falling of this armature the contact springs 237 and 291 will be connected for a moment. Vhen the armature of c vr has fallen entirely back the spring 291 will press the spring 236 away from 237 thus breaking the connection between 237 and 291.'` While the connection lasts a current will flow from the 'negative pole through 220, 230, 237, 236, 291, 290, off-normal switch 238, which is closed when the wipers are lifted out of their normal position, 226, 247 to earth. This energizes the rotary magnet 247 which turns thewipers ga, r/ Z, g c of the group selector around one step and thereby causes the rotary off-normal switches and 256 to be closed. The switch 256 connects an interruptor 257 to the rotary magnet so that lmpulses now commence flowing from the negative pole through 257, 256, 229, 226, rotary magnet 247 to earth and the rotary magnet causes the `brushes to travel over the sets of fixed contacts connected to trunks oas, @53, 'v0.3 until a trunk leading to an idle second group selector Gr W' is reached when a current will flow from the positive battery pole through the test relay 248, test wiper gc, 2103, 300 to earth.

`The test relay 248 and the release relay 300 of the second group selector both attract their armatures. The former opens its contact 229 land thus interrupts the circuit of the motor magnet 247 and by its contacts 226, 227 it also shifts the change over circuit 290 from the rotary magnet to a relay 249. The stepping or measuring circuit 295 is shifted from the vertical magnet 246 to the brush g a the connection to the brush g a being made through contacts 225 and 270.

By its contact 228 the test relay 248 short circuits a part of its winding and thereby reduces the potential on the test o0, to such an extent that no other first group selector will be. `able to establish a connection with the second group selector Gr WH.

An idle group selector in the third thousand group now being selected and found the calling subscriber proceeds to select the desired fourth hundred group by causing four interruptions of his line loop with the aid of his switch controller. This causes four oscillations of the line control relay armature and each time this armature falls back an impulse flows from the negative pole through 220, 231, 234, 295, 225, 270, g a, o a3, 307, vertical magnet 305 to earth. The vertical magnet moves the brushes ga, gb, gc of the second group selector G XV up to the fourth bank contact row. When the brushes are raised out of their normal position a contact 303 is closed which prepares the circuit of the release magnet 304 which is open at this time at the contact 302.

. After the calling subscriber has caused the series of four interruptions of his line loop another interval ensues during which the loop is steadily closed and the line control relay armature is steadily attracted. The change over relay c 7 is tllenvsteadily short circuited by the contact 2'33'of the line con"- trol relay and allows its arrnfature to drop back and to close the change over circuit which may be traced from the negative 'pole through 22o, 23o. 237, 236, 291, 290,238,227, relay 249 to earth. The relay is energized and sends a change over impulse from the negative pole through 252, 296. 277, (7 b, 'u 51,. 312, 313, 310, rotary magnet 306 of the second group selector G lV to earth. The rotary magnet in'unediately turns the brushes ga, gb. gc one step and thus causes the opening of off-normal contact 313 and the closing of oi-norma-l-contact 315. Thev impulse sent over-sth 313 and the. closure of an independent vcir# cuit for the rotary magnet by the contact 315.

When the' change over relay 249 was en"- ergized it not lonly closed the change over circuit but also, the circuit of a slow-acting ifel'ay`250-- (negativepole, 253, 250 to earth).

This relay.` closes a vcontact 254 and when on the immediate opening of thev change rover circuit 290, the relay 249 is denergized, the.

ringing current Source 268 is applied through 258, 254, 251, 206, 277 to the line c b3 until .the slow-acting relay allows its armature to fall back so as to yout off the ringing current -at its contact 254. Although the ringing current is applied to the line v b3 no ringing current will flow because the change over circuit from 296, 277, g b, 'v b3, 312, 313, 310, 306 to earth was interrupted the moment the relay 249 attracted its armature and sent an impulse through the rotary magnet 306 causing the contact 313 to be opened in the manner already eX- plained.

The circuits are so arranged that a closed circuit through which ringing current will flow upon the ringing machine being applied through 296 to the line c b3 will'be found only after vthe inal selector (connector) has made connection with the wanted line and has found this line idle. Under these circumstances the ringing current. machine will send ringing current to the called subscriber until this subscriber in responding to the call removes his receiver `from its switch hook and thereby causes the Ting-ing current -to be strengthened suiiciently to energize a relay 264 at the group selector which then causes the ringing current to be cut off and the calling and-called ends of the talkin'gcrcuit to be" coirnected' test relay of the -inal selector or connector.

According as the wanted lineiszidle' oribusy 'the test relay will cause ringing current to be applied to it or not. If it;werey desired with ,circuits of this kind to, placethegring-m n currentjsurcefatejgroup'selector some circuits: would have to be provided` by whlch the influence of the test relay at the linal selector` is transmitted back to the group selector in order to connect the ringing current to` the wanted line. v y

ln .in rer'itioril these lSpecialv circuits Vfork ij-the test frel'ay of the-'final Se# eeterr po -the means at the group selector for'connect ing the ringing current are avoided.v According to this invention the r1ng' .ing'currentis applied momentarily to the fll-inmatliich .isbeing eXtended to ,thev want-edT subscriber .at-'each change' over impulse.v The permanent connectionl 'et ,the *ringing* cur-'A rentto themline is, however, made dependent lon the line extendingtothe'wanted subscriberl being found closed. If the vline is found closed the ringing current will actually How' and in flowing it causes circuit changes at the group selector which result in the tentative application oft-he ringing current being converted into a steady connection of the saine which lasts until the wanted subscriber responds to the call.

It has been previously explained that the disconnecting of the tentatively applied' ringing machine 268 is effected by the dropping back of the larmature of the slow-acting relay 254 shortly after the closure of the circuit of the rotary magnet 306 ot' the second group selector Gr WVU because on account of the opening ofA contact 313 no closed circuit exists in which a ringing current can flow `from the ringing machine. The circuits by which the ringing machine is ysteadily connected in the case of being applied to a closed, circuit will be explained later.,

The rotary magnet 306 which is energized by current impulses from the negative pole through 314,315, 310, 306 to earth turns the wipers ga, gb, of the second group selector causing them to brush over sets ot the fixed bank contacts leading to the fifteen two-way switches V S through trunksaauo, 11300, 031,0 until an idle trunkeig reached. If a trunk a300, bm, 0300 is idle the two-way switch Figs. 3 and 4 associated therewith will be in its normal position and it-s contact 130 will be closed.

'The trunk (am, 5,00, 0300 to which the group selectorG WH extends the connection of the calling subscriber will, of course,

Y. lead to a different two-way switch than the one whose brushes are connected to the calling line. But as the circuitsof all the twoway switches are'alike the events which'take place at this stage of the connection of the calling subscriber' may be explained with the aid of Figs. 2, 3, 4.

1- The two-way switches of the selected hundred group which are already being used Vfor, other connections will appear` busy to the vhunting group selector on account of their switches 130'be11'1g open. F.Il'ie momentl they brushes'of the group selector strike a.free trunk a current will flow through the test relay p fr; from the negative battery pole through 301, p r2, g c, 2300, converting relay R of the idletwo-way switch inthe dejsired hundred group, closed switch ,130 to" l i earth. The" relays frzndS R are' bot-h en- 'ergizedl The former opens the* circuit of l At contact 118 the battery the rotary magnet 306 at its contact 310 and by closing its contact 309 it short circuits a part ot' itsI winding andthus lowers the potential on the lest. wire (am, so as to render the sei/.ed trunk busy. B v closing itsA contactsl 308, 311 the. test relay p yl', extends the talking circuit "u Us, '0 b3 to the two-way switch Figs. 3 and L1.

The converting relay S R by-shifting its armature contacts 'converts the two-"way switch from a line inder to a final selector. By openingits contact 111 and closing the cont-act 112 it disconnects the starting wire two-way switch .and i S lV from the seized extends it to the wire S 7, leadingft the next two-way switch in the 4hundred group so that the next call arising in this group will be passed on to this next two-way switch. By .closing its contact 113 the converting relay connects the change over wire bm to the change over devices, 190, 193 which at a later stage change the connection of the selecting wire a300 from the tens or secondary motor magnet Z M to the units or primary motor magnet E M of the twoway switch. By the closure ot' contact 114 the selecting wire w30, is connected tothe tens magnet Z M (through 139, 160, 158, Z M, 159 to earth). By opening` or contact 115 the circuits of'magnets Z M and E M which are ordinarily connected to the common wire 193 leading from the interrupter 168 are separated so that now each of these motor magnets can be controlled separately. At the contact 11G the release wire leading to the associated selector finder or group selector is broken in order that when this wire is earthed on the breakingdown of the con ncction in the manner to be described a momentary' closure of' the circuit of the rotary magnet is prevented. This momentarily closed circuit would extend from the negative pole through 218, 210, 206, 202, 217, or.V Z, 195, 194, 129, 128 to earth. At the contact 117 the battery lead to the relays 79 r, s 7' is openedin order that, when the brushes of the two-way switch are moved into connec,

tion with the wanted line, the touching of earthed guide wires by the brushes p b, s I; will not cause the said relays to be energized.

lead from the interrupter 168 to the wire 161 is disconnected in order to prevent impulses flowing through 118, 164, 135, h (L, 200 203 to the starting relay 205 of the selector finder H S on the shifting of the switch O S1 which happens when the two-way switch is moved out of its normal position. The contact 197 opens current path from the selecting wire a300 through 139, 131, 161, 135, 200 to the starting relay 205 and at contacts 119, 121, 123, the lines v al, fvselector inder are disconnected. Through contacts 120, 121 the talking wires inthe two-way switch are disconnected from the Finally the converting 1) o c1 leading to the Y selector finde-r and connected-to the trunk extending from the. partly established connection of the calling subscriber. By the opening of-the contact 121 the ordinary circuit ot the test relay t r is broken and this relay is converted by the opening of the contact 125 and closure y of contact 126 into a the condition of the wanted line that will presenti be selected by the two-way switch.

By closing the contact 127 the converting relay S 4R closes a locking circuit for itself which is independent of the switch 130.

relay S R. moves on beingenergized the contact spring 129 but 1n so doing no connection is made between the. contacts 129, 128. These contacts are closed only when the relay S R is denergized and they then cause the energization of a release relay r Z as will be more fully described later. The contacts 116, 129, 128 are-so adjusted that the contact 116 is closed only after the contact between 129, 128 is opened so as to prevent an impulse flowing from earth through 128, 129, 195, 116, 217,- 202 to the rotary magnet 206 of the selector finder.

Vlhen the converting relay S R is energized and has produced the circuit changes just described the calling subscriber sends in the tens selecting impulses by causing a number of interruptions of his line loop that corresponds to the tiens digit of the wanted line which in this case is 6. trol relay 280, Fig. 6, lets its armature execute six oscillations. Each time the armature falls back an impulse ows from the negative battery pole through 220, 231, 234, 295, 225, 270, g a, c as, 308, gla, a300, 114, 139, 158, tens motor magnet Z M,'159 to earth. By these six impulses the set of brushes b al, Y) b1, Z) 01 of the two-way switch is stepped around to the sixth set 7c e which is connected to the sixth brush set, fi. e. the set of brushes b a, b I), b c, that travels over thel contact sets 7c s in the sixth row or sixth tens group. The desired tens Agroup is now selected.

In order to select the individual line in the selected group of ten lines all the brush sets ba, I) b, Y) c of the two-way switch are moved five steps. The sixth brush set b a, b b, b c will then rest upon the fifth set of bank contacts in its contact row this being the set ot bank contacts that belongs to the wanted line No. 34.65. The desired line is now selected.

The other nine sets of brushes b a, l) l), b G will also each be resting on' the fifth contacts sets 7c s in their respective rows, but these brush set-s have no connection with a brush set I) (L1, I) 7/1, c1 so that they do not establish any connection with the subscribers lines on which they are resting.

A detailed description of the swltching the llast group selectnnin.-

test relay for testing v The line confunctions which take place in sett-ing the brushes b a., l) 7), I) c of the two-way' switch onto the desired line will now be given.

After the series of' tens selecting impulses is sent in the calling subscriber-s loop is again steadily closed and the steady Vshort circuiting of the change over relay c i caused hereby results in -the falling back of the changeover relay armature. A change over impulse then flows from thc negative pole through 22o, 23o, 2a?, 23e, 291, aas. 290, 227, relay 219 to earth. The relay 219 attrae-ts its armature and closes a circuit extendingfrom the negative pole through 252, 296. 277, f/ e 7) 311, [/17), bm, 11.3, Fig. 4, 152, change over relay 190 to earth. The change over relay is energized and immedi- -ately opens the change over circuit at 152 so that the ringing machine 263 applied to the change over circuit through 254, 251 can not send out any ringing current and will be cut off again by thel dropping back of tlie` armature of the slov-acting relay.

The change-over relay 19() closes a locking circuit for itself from the negative. pole through 151, 153, 19() to earth. The switch 151 is closed when the secondary tindcr Z T is moved out of its normal position.

At its contact 139 the change over relay separates the selecting wire (am, from the secondary motor magnet Z M and connects it through contact 138 and through 196, 162 to the primary motor magnet E M.

()n the calling subscriber now sending the five units selecting impulses the armature of the line control relay 28() drops back tive times and tive units selecting impulses flow through 220, 231. 23-1, 295, 225, 270. ,f/ a, o (1. 308, ga, am, 111, 13S, 196, 162, primary motor magnet E 5M, 163 to earth` these im-A pulses causing the brush sets 7) (L, 7) 7) o to be moved to theififth bank contact sets and to select the desired subscribcrs line in the manner already described.

After the last series of selecting impulses has gone in the line control relay 28() keeps its armature steadily attracted so asv to dee/nergize the change over relay c r again by i short circuiting it. The relay 249 is then momentarily energized and a test in'ipulse fiows from the negative pole through 252, 296, 277, g Z1, 'v 74 311, (/17), bm, 113, switch 15() which is closed the moment the primary finder is moved out of its normal position, 149, relay 193 to earth. The relay 19.3 is energized and by opening contact 149 disconnects itself from the Change over wire 71,00. But it also closes a test circuit extending from the positive pole through 198, 146,

, la7, relayt r, 126,1@v c, b c1, 7i c, test Wire ,fgktnot shown-in the drawing but similar `tto the'test wire of the calling subscriber) cut off relay c -r of the desired line No. 3465 to the negative pole of the exchange battcry.- If the wanted line is free the rel-ay 2H', which now acts as a test relay, Will be immediately energized and will extend the lines a300, 7100 to the line of the wanted subscriber by closing its contacts 1111, 142. The

ringing machine, which is applied by the contact 251 of the slow-acting relay to the line bm after the change over impulse sent through contact 252 ceases, now sends out a rineinfr current before the sloW-actino 75 34656, bell of wanted subscriber N 3465, go

31657;, (43,65, 7) a, Z) al, o a, 141, 120, am, gla, 398, lr a3, g a, 279, 225, 29o, 298 to earth.

By the immediate flowing of the ringing current the steady connection ofl the saine to wanted line is effected by means of a relay 25S which is energized by the ringing current and closes a ringing current path which is independent of the conta-ct 251 of the slim-acting relay, this path leading through 259, 260, righthand winding of relay 299,296,277 to the above-described ringi ing circuit. The relay 299 is now energized and the circuit including relay 258 is broken at 260 ywhich causes the relay 258 to open its armature contact 259 and to permanently the wanted subscribers ringing circuit. But

if the interrupter happens to have closed the contact 266 at the moment the relay 258 is cut off, the ringing current will not flow through the line of the wanted subscriber but through 266, 263 and the left Winding of 299. It is thus seen that in any case the one or the other Winding of 299 is energized. If the contact 265 is closed the ringing current flows through the relay 261 and the right handl Winding of 299 to the Wanted line, but if the Contact 266 is closed the Whole ringing current flows through the left Wind ing of 299 and there will be a pause in the ringing of the wanted subscribers bell.

When the called party responds by re- 12o moving his receiver from his switch hook the ringing current flowing through the relay 264C is strengthened sufficiently to cause this relay to close its armature contact 263.

A. current then flows from the negative pole through 263, connecting relay 273 to earth. The relay 27 3 thereupon interrupts the flow of. ringing current at 277 so that the energi- Zation of the right winding of 299 ceases before the left Winding is renergized. The 13,0

If thel interrupter 267 100 relay 299 is therefore denergized and the ringing machine 268 is cut off at 261l 262.

By closing its contacts 271, 276 the relay 273 extends theline of the calling subscriber to that of the c alled subscriber and disconnects selecting and change over circuits at contacts 270 and 277. f-

The relay 273 closes a locking circuit for itself 'by its Contact 272 (negative pole, 255, 272, 273, earth) and by its contact 269 it momentarily short circuits a part of the winding e 1 and thus momentarily strengthens the current in' the meter circuit (fu c2, v c1, 123, 143, c c, b c1, Z) c, 012, 212,- negative pole) so as to make the meter 212 attract its armature and register the conversation.

In order to `cause t-he meter circuit to be only momentarily closed by the energization of the relay 273 so as not to impair the busy condition of the test wire fv 02 the contact 269 is made like the contact 119, 120 of the call regulator A R, Fig. 2. This is more clearly shown in Figs. 8 and 9. 1n Fig. S 273 represents the end of the armature that is moved in the direction indicated by the arrow 274 when the relay 273 is energized. The end of the armature is round and glides, along the right hand oblique surface` at the end of the contact spring 269 so as to move 269 toward the left and against the -contact spring 269: When the armature is fully attracted its end will be located above 269 as indicated by the dotted circle 273. On the denergization of the relay 273 the round end 273 glides along the left side of the oblique end of 269 forcing it'farther away from 269 instead of toward 269."

The aiecting of the busy condition of the line o 02 can also be prevented by using a contact 119, 120 which causes the momentary yclosure of the meter circuit on the deenergization of relay 273 at the finish of the talking connection. In this case a similar arrangement to that illustrated in Figs. 8 and 9 is used but the end of the armature is arranged soas to push the spring 269 away from 269 when it is attracted and to' push it against 269 when it falls back. In other words the end of 269, instead of running in slanting direction from its top end downward toward the left, would run slanting direction from its top end downward toward the right.

When the calling and called ends-fof the talking circuit are Iconnected at the contacts 1 271, 276 a circuit is closed including the relays 278. 279 and extending from earth through 278, 271, g a, c a3, 308, gla, a300 to the two-way switch which has established the connection with the wanted line, 120, 141, c c, b a1, a of the sixth set of brushes,

(1.111,1, 346541., S2111, 3465?), 191165, Z) b, 71 b1, v b, 112, 12e, 53,0, gli), 311, t b3, g I), 276, 279 to The relays 278, 279 are the negative pole.

excited; 279 closes its armature contact 240 and 248 opens its contact 239.

The calling subscriber is now connected to the called subscriber over the following path: S12, 12a, a12, b a, al of the two-way switch which has connected to the calling line, b a1, c a, 141, 119, 215, fw a, c a 2, c 01, 271, g, a, fv, a3, 30S, gla, a 200, two-way switch V S in the called hundred group, Contact 120 of the converting relay SR ofthis I 280 will be de'nergized and the release relay r 1 will 'be steadily short circuited. .The latter relay will then allow its armature to drop back and close the release circuit (earth, 235, 245, 223, negative pole). rlhe release magnet 245 will be energized and will cause the first group selector to be restored t its. normal position. The release magnet also opens its armature contact and thereby'denergizes the relays e r and p Ir h. The relay p 1 it lets its armatura@J drop back, thus opening its locking circuit at its front contact 212 so that, until the starting'relay 205 is energized again, no reenergization of the relay o fr it can take place. By the contact 210 the circuit'oi the rotary magnet 206I of the selector finder is closed (negative pole, 218, 210, 206, 209, earth) and this magnet now rotates the brushes w as, wb, w c in a forward direction,.until they reach their normal position, when the off-normal switch 209 will be opened and the circuit of the rotary magnet 206 interrupted.

The denergization of relay p r h causes the closure of its armature Contact 217 and the completion of the release circuit of the two-way switch V S which made the connection with the 'calling line this release circuit extending frorn earth through 209, 202, 217, a Z, 116, 195, relay r Z to the negative pole. The release relay r Z ofthe twoway switch is thus energized and closes a locking circuit for itself which may be traced from the negative battery pole to r Z, 137, 107 to earth. At its contact 136 the release relay opens the locking circuit of the relay t r. This relay is then denergized and closes at its back Contact 131 the circuit of the magnet E M (negative pole, 16S, 108, 155, 118, 157, 131, 115, 162, E M, earth) which remains closed until the driving' device D of the primary finder reaches its normal position'and terminate the connection by replacing his disconnects the interruptor 10S from the motor magnet E M by opening the conmet 1084. f

The motor magnet Z M of thel secondary finder is completely disconnected from the circuit of the motor magnet .E M of the primary iinder at contact-1951 of the restoring rel-ay fr Z in order that the two finders may move independently of each other into their lnormal position.

The independent restoring circuit ot the motor magnet Z M is closed by the contact 1961 of the restoring relay 1* Z and extends from the nega-tive pole to intcrrupter 1971, 1961, 1671, Z M, 159 and to earth. r1`he moment the secondary finder reaches its normal position the contact 1671 is opened and the motion oil the tinder is stopped through the interruption ot' the circuit of the magnet Z M.

In order to prevent interruptions of the circuits of the magnets ll M, Z M by energizations ot' the test relays p 1, s i" caused during the travel Vof the brushes p Z), s Z) into their normal positions by their striking earthed guide wires the 'battery lead to these relays is kept open by thecontact 134 of Qthe restoring relay?" Z unt-il this relay is deenergized. r1`hc restoring relay i-s, however, not denergized until the two-way switch reaches its normal position and opens the locking circuit of the restoring relay fr' Z by severing the contacts 107 and 167.

To prevent the flowing of impulses from 16s till-@ugh 108, 155, 11s, 15e, 151, h a, 200 to the starting relay 205 when the relay i j) r h is deenergized andthe contact 200 closes the armature contacts of p r ZZ are so adjusted that 200 remains upon until shortly afterA the closure of 217 e. until shortly after the energization of r Z and until the opening of 135 by r Z. By this means current' impulses are prevented from flowing from 168 through 108, 155, 118, 156, 161- to the starting Wire h adoring the restoration ofthe two-way switch which would cause a displacement of the selector finder H S.

The. second group selector Gr N11 is released as soon as the firstgroup selector vis restored and its brush g c breaks its connection with the trunk wire fu c3. The relay 300 of the second group selector is then deenergized and closes the circuit of the release magnet 3041 (negative pole, 302, release magnet 301, 303, earth). .which.thereupon releases v the second :groupqselector. y At the momentlille 'release eircuitr'is: closed the test circuit oflp rg, opened at.301 so as to prevent any vvenerg'ljization of the testvrelay p r2 while elle the brush g1 c travels over the bank contacts of other trunks 63,00 during the restoration4 of the selector.

The moment the contact arm g1 0 of the -second group selector leaves the trunk 030 leading to the called hundred group the converting relay b' R of the two-way switch in this group that was used for t-he talking connection is denergized and on its armature falling back the Contact A128, 12Stis momentarily closed. This causes the euergization of the restoring relay 'r Z'associated with this two-way switch, the restoring circuit extending from earth, 128, 129, 191, i' Z to the negative pole.

The deinergization of the converting relay S It results in the opening ot' the circuit o1 the test relay t -r Searth, 110, t i', 126, fr c, Z) c1, Z) c, CMS, c 113465 by the Contact 126.

The two-way switch used for establishing the connection with the wanted subscriber is now restored in the same manner as the two-way switch that connected to the calling line, the restoring functions of which have already been described.

It`will be remembered that the magnet E M is energized by impulses from the negative pole through 168, 108, 11S, 157, 131, 115, 162, E M, 163 to earth and that the magnet Z M receives its restoring impulses from the negative pole through 1971, 1961, 1671, Z M, 159 to earth.

It' the called subscriber is the first to replace, his receiver on the switch hook at the f tion extending toward the calling subscriber and toward the called subscriber.

Instead of using a slow-acting relay 27 9 and a quick acting` relay 278 Jr'or the act of restoring by the called subscriber a single relay provided with contacts like 119, 190 of the call regulator may be used. This contact could bel arranged to be closed not when the restoring relay (e. g. 278) is energized gut when this relay lets 'its armature drop f ack.

If the wanted line is'busy at the moment 'the two-way switch is set onto the wanted line, the relay tr will not be energized as previously described and hence thetalking leads of'the calling subscriber will not. be connected through the contacts 141, 1512 to the line of the wanted subscriber.

A feature. of the meter circuits used in the present system which was not mentioned in the above description will now be pointed out: 1

AIt was shown that the actuation of the meter of the calling subscriber is caused by strengthening the current fiowing in the wire cl2, this strengthening being produced by partially short circuiting the winding of relay e 'r by means of contact 269. i Now, when a two-way switch is used to establish a connection with a wanted line, the energization of the relay t 11 of this switch and the 'partial short-circuiting of this relay will also produce a strengthening of the current in thewire 03465 of the called subscriber. But the alteration of the current strength will be balanced by the resistances wm, 'wm

. so as to prevent the called subscriber-s meter over wire.

`190 to earth.

Y 167 which closes being actuated.

Mention will now be made'ofv a detail regarding the ringing and change over circuits:

vIt will be remembered that the change over relay 249 denergized for a moment at the end of each series of selecting impulses and momentarily connects the negativevpole through 252 and 277 to the change ringing current machine 268 is connected through 254, 251, 277. to the change over wire, but a current does not flow through it because the contact 313 is immediately opened by the operation of the rotary magnet 806. But it is possi'ble that the group selector G W will find the first or second trunk a300 idle and that yin such a ca the test relay p r2 will very soon extend the change over wire o b3 to the final twoj-Way switch by closing the contact 31,1. This extension of the change over wire would then possibly take place before relay250 re-opens its contact nects the ringing machine. Thls would` re sult in the steady application of the ringing machine to the change over circuit because a ringingcurrent would {iow `from earth through 268, 258, 254, 251, 296, 277, g b, lv b3, 311,\jg1b,^- 6300,11?) (this contact would berclosed by the energization of S R) 152,

i In order lto prevent this undesirable -flowing' of ringing current a switch is'preferably provided at the point 1991 indicated by the cross in the two-way switch which is closed only when the calling subscriber commences to send in his tens selecting impulses. By that time the slowacting relay 250 will be sure to have found time to open its contact 254.

The switch at'point 199'1 may consist of a contact comprising two springs similar to the moment an impulse is sent through the tens magnet ZM.

It was assumed -'n theI case of the above connection between a calling and a` called subscriber that a two-way switch that is associated with a selector finderextended the calling subscriber-s line to a first group selec- Immediately afterward on thel droppingy back of the armature of 249., the v the slow-acting' 254 and discon' tor. If, at the time the calling subscriber makes a call, the next idle two-way switch into an associated irst group selector and the starting wire extending' from point 157 through 135 will be unnecessary.

The release wire a Z instead `of Vpassing through contact 217 will be connected directly to an armature contact of the release ymagnet 245 of the first group selector and on the energization of the release magnet the restoration of the two-way switch will be initiated `by the earthing of the restoring wire Z.

Another point will be mentioned in connection with regulating' of the incoming calls by the call regulator. Itwill lbe re.- membered that thel call regulator ordinarily prevents two calls from being simultaneouslypassed on to the two-way switches of a hundred group.. The call regulator will perform its function perfectly as long as not more than two calls comev in at the same or almost the same instant. This will aai."

generally be all that is required in a practical system. That three or more calls will come in `at the same instant is almost out of question. Even this contingency can however be providedfor by arranging a special relay common to each group of subscribers which will be excited if more than one subscriber calls in the intervall of about a second during which a two-way switch is in the act of making `a connectionwith a' calling line. The special common' relay will then cause relays,v yof which one is associated with each of the lines vthat happens to call in the above mentioned interval, to be energized and to connect these lines to a special signal, while disconnecting venting two or more subscribers from simultaneously earthing the guide wires and possibly causing inefectivedine finding operationsof the two-way switches. The special signal would cause the subscribers who sent in simultaneous calls to hang up their receivers and to thus restore their lines to their normal idle condition. The subscribers would then wait a few seconds before making their connections..4

Means by which the specialsignal may be given are known in the art so that a detail description of the-same appears unnecessary.

Having now particularly describedv and ascertained the nature of the said invention, 

